Demand measurement.



J. R. CRAIGHEAD.

DEMAND MEASUREMENT.

APPLICATION FILED SEPT, 2. m6.

Pafentvd June 11, 1918.

Fig. 2.

15% :m n @Mw va t t eCt fi Vo INN .mwflH To all whom it may concern:

UNITED STATES PATENT OFFICE.

JAMES R. CRAIGHEAD, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC-TRIO COMPANY, A CORPORATION 01' NEW YORK.

DEMAND MEASUREMENT.

Specification of Letters Patent.

Patented June 11, 1918.

Application med September 2, 1916. Serial-No. 118,256.

Be it known that I, JAMES R. CRAIGH AD, a citizen of the United States,residing at Schenectady, in the county of Schenectady, State of NewYork, have invented certain new and useful Improvements in DemandMeasurements, of which the following is a specification.

My invention relates to demand measurements, and particularly to themeasurement of electric demands. More specifically the invention relatesto demand apparatus for indicating or recording the demand made by anelectrical installation upon a source of electric energy supply.

One of the objects of my present invention is to provide an improvedmethod of determining the demand of an electrical installation. Anotherobject of the invention is to provide an improved demand appara tusparticularly adapted to carry out the method of the invention. A furtherobject of the invention is to provide an improvedrecording apparatusfrom whose record is readily ascertainable the demand of an electricalinstallation during a predetermined period of time beginning at anydesired actual time. Qther objects of the invention will be brought outin the course of the following discussion.

A well known type of electric demand apparatus measures the demandduring each of a plurality of equal time intervals, and records thedemand for each time interval or indicates in some suitable manner themaximum demand during any one of a number of such time intervals. Inusing such apparatus, the highest actual demand is frequently dividedbetween two successive time intervals, and hence the measured demand foreither interval is lower than the actual maximum demand. In other words,where the beginning of the predetermined time interval of demandmeasurement is arbitrarily fixed, a peak demand may easily be dividedbetween two time intervals, instead of being included in a single timeinterval, as it should be in order to give the true maximum demand forthe predetermined length of time.

The improved method of demand measurement of my present inventionconsists broadly in the production of two similar records whosecoordinates are energy consumption and time, and in the arrangement ofthese records so that the coordinate of any point of one record with resect to the amount of energy consumed ist e same as that of thecorresponding point of the other .In other words, the two records are soarranged that the coordinates with respect to the amount of energyconsumption of corresponding points on the two records are the same,while coordinates with respect to time of corresponding points on thetwo records are displaced an amount corresponding to the time intervalof demand measurement. Then, for any particular time, the demand duringthe predetermined time interval is determined by comparing thecoordinates with respect to the amount of energy consumption of twopoints on the two records havin the same coordinate of time. Theimproved demand apparatus of my present invention is particularlyadapted to carry out this method, and, accordingly, produces a compositerecord from which the demand during a predetermined length of time.beginning at any desired actual time can be easily ascertained. By theimproved method and apparatus of my present invention, the true maximumdemand for the predetermined time interval of demand measurement iseasily obtained, where it might frequently fail tobe properly recordedin present day-types of apparatus in which the demands for successiveperiods of time are arbitrarily recorded.

The preferred construction of demand apparatus of my present inventionin its complete form comprises a device adapted to produce on a timeactuated record sheet two similar records of the amount of energyconsumed or metered. These two similar records are displaced from oneanother in till is desired to know the average demand. The differencebetween the coordinates with respect to the amount or? energy consumedof two points, one on each record, having common coordinate of time isthen a measure of the demand during the predetermined period of timebeginning time represented by such common cotirdinate of time.

The novel features of the invention which believe to be patentable aredefinitely indicated in the claims appended hereto. The invention itselfand the construction and mode of operation or" demand apparatusembodying the same will be better understood from the followingdescription taken in conjunction with the accompanying drawing,

. in which Figure 1 is a diagrammatic view in perspective of a demandapparatus embodying my present invention; and lg. 2 is a portion of arecord obtained from the apparatus Fig. 1..

The demand apparatus illustrated in it comprises an integrating electricwatthour meter having a rotatable shaft 5. The watthour meter iselectrically connected to measure the amount of electric energy suppliedto translating devices 6 by a source oi alternating current l. Thewatthour meter is of the well known induction. meter type having seriescoils 8 and a po tential coil 9 adapted to produce a shifting magneticfield Within whose influence is arranged dislr armature 10, of aluminumor other *uitable material secured to the meter Permanent magnets dampthe rotation of the disk armature 10 in a well understood manner.

The meter shaft 5 is operatively connected, as for example by suitablegearing, to a gear 12 secured to a shaft 13. A gear id is also securedto the shaft 13 and is arranged to normally mesh with a sector-shapedgear 15. The sector-shaped gear 15 is rotatably mounted on a pivotedshaft 16 and carries a depending arm 17. Two recording devices 18 aresecured to the cross arm idol a T- shaped member 20. The standard of thel-shaped member 20 is pivotally attached to the arm 17.

The recording devices 18 may be of any suitable kind for making agraphic record on a time actuated record sheet as chart :21. Thus therecording devices 18 may be pencils, or self-inking pens, or may bemetal styli, cooperating with suitably prepared paper. The record sheet21 maybe moved at a uniform speed in any suitable manner. in. thedrawings, T have shown, for the purposes of explanation, the recordsheet 21 wound on a drum 22 rotated at a uniform. speed by aclock-driven member 23.

The recording devices or markers 18 are spaced from each other in thedirection of movement of the record sheet 21. These income two recordingdevices thus produce two similar records. In tact the two recordsproduced by the recording devices 18 are identical, except that one isdisplaced from the other a predetermined distance in the direction ofmovement of the record sheet. The distance, in the direction oilmovement of the record sheet, between the two record ing devices 18 isdetermined by the time interval for which it is desired to know thedemand. Thus, the recording devices 18 are separated by distance equalto the amount of movement or the record sheet 21 in the predeterminedtime chosen as the time interval of measurement of the demand. Thus,where the time interval of demand measurement is thirty minutes, thedistance between the recording devices 18 is the distance which therecord sheet :21 moves in thirty minutes. It will oi course beunderstood that more than two recording devices may be operativelymounted on the cross arm 19, so that a plurality of pairs of recordseach having difierent time intervals may be obtained. Preferably, therecords produced by the two recording devices 18 are characteristicallydifierent, so that the records may be distinguished from one another,Thus, difterent colored inks may be employed to prevent coniusion or"the two records.

Z-Vhenever electric energy is consumed in the translating devices 6, themeter shaft 5 rotates at a speed which is a measure of the rate ofenergy consumption, and the total revolutions of the of the integratedenergy consumption, as is well understood in the art. The recordingdevices 18 are moved transversely of the record sheet 21 at a rateproportional to the rate of rotation 01E the meter shaft, and hence thetransverse movement of the record ing devices from their initialpositions at one side of the record sheet is a measure of the amount ofenergy consumed in the trans lating" devices since the recording devicesoccupied their initial positions. The two records thus give anindication of the total watthours of electrical energy consumed in thedevices 6 up to any point of time, but one record is displaced on therecord sheet by a distance corresponding to the time for which it isdesired to indicate the demand.

The actual demand for the desired time interval at any particular timeis represented by the transverse distance between the two records. inFig. 2 of the drawings, l have designated the record produced by theforward recording device by the heavy line A, while the record producedby the rear recording device is designated by the light line B. Thedemand at any time for the time interval of measurement is thenrepresented by the vertical distance, as viewed in Fig. 2, between therecord lines A and B.

The greatest transverse distance between the meter shaft are a measurerecord lines A and B obviously represents the maximum demand. Thus, atthe time represented by t on the record sheet, the demand for thepredetermined time interval of measurement is represented by the lengtof the dotted line d. v

The principle of operation of my improved demand apparatus will perhasomewhat better understood by consi ering at greater length just whateach of the two records A and B represents. Take, for example, theposition of the recording devices 18 at the time t. The forwardrecording device is at the position designated 7 on the record sheetwhile the rear recording device is at the position designated 7'. Attime t, the forward recording device is at position f While the rearrecording device is at position r. The difference between times t and t,is the predetermined time interval of demand measurement, say, forexample, thirty' minutes. Then, the amount of energy consumed in thethirty minutes beginnin at t is the difference in distance of the pointsf and f from the zero or initial line of the record sheet, and obviouslythis difference in distance is the length of the line d. So the lengthof the line d represents the amount of energy consumed in thetranslating devices 6 during the time interval beginning at t and endingat or in the case assumed, during a time interval of thirty minutesbeginning at time rl. Similarly, any vertical distance between therecords A and B represents the amount of energy consumed, that is thedemand in terms of integrated energy, in the predetermined time intervalof measurement beginning at the time corresponding to the position ofthe vertical distance on the record sheet. As previously pointed out,the maximum integrated demand during the characteristic period ofmeasurement of the device is found by determining the greatesttransverse or vertical distance between the two record lines A and B.'An inspection of the entire record as a whole will generally indicateabout the location of the maximum demand. For example, when theintegrated demand over the devices characteristic time interval ofmeasurement is zero, the two records A. and B become coincident, asindicated at 0 on the record shown in Fig. 2 of the draw ings. When theintegrated demand is relatively low the slope of the two records is verygradual, and as the'demand increases the slope of the records increases.This affords a quick and convenient means for picking out the points ofrelatively lar e demand, and the maximum demand can determined bymeasurement and comparison of such points. In the record of Fig. 2, themaximum demand occurred during the time interval beginning about at 15,,and the magnitude of the integrated demand over the devicescharacteristic time interval is reprc transverse distance between thetwo records A and B and hence the maximum demand.

The two records A and B produced by the recording device 18 are ineffect continuous records, but the width of the record sheet becomes alimiting factor with respect to the continuous character of theserecords. Thus, in order to utilize the record sheet to the bestadvantage, and thus to do away with the necessity of too wide a recordsheet, I preferably provide the apparatus with means for intermittentlyreturning the recording devices to an initial or zero position at oneside of the record sheet. Thus, when the recording devices have traveledsubstantially the entire distance transversely of the record sheet, Ireturn the devices to their initial positions. In the apparatus shown inFig. 1, this is doneby interrupting the operative connection between themeter shaft and the sector-shaped gear 15, when the meter shaft has madea predetermined number of revolutions, and then returningthesector-shaped gear 15 and cooperating parts to their respective initialpositions, as determined by a fixed stop 30, by means of a spring 31.

Thus, the spring 31 normally tends to move the recording devices 18until the arm 17 engages the fixed stop 30, whereby the initial or zeropositions of the recording devices are determined. A movable contact 32secured to the gear 12 cooperates with a fixed contact 33 each time themeter shaft has made a predetermined number of revolw tions tomomentarily close the circuit of an alternating current relay 34:. Whenthe relay 34: is energized by the engagement of contacts 32 and 33, itsarmature 35 is attracted, thereby raising the end of the shaft 13carrying the gear 14 to such an extent that the gear 14 is operativelydisconnected from the sector-shaped gear 15. The spring 31 then returnsthe recording devices 18 to their initial positions. It will be evidentthat the demand at any time during the interval represented on therecord sheet between the lines made by the return of the recordingdevices to their initial positions,

for example during the time interval 4, 29,,

is the sum of the distances of the two records Band A from the initialand terminal lines, respectively, at the sides of the record sheet.

Thus, the demand for the time interval of measurement beginning at time25;, is represented by the sum of the lengthsof the two lines at and d".

carry out the method of demand measurement of my present invention, andit now consider this apparatus to he the best means for practising themethod. lit will of course he understood, however, that the method mayhe practised in other Ways than mentioned in this specification. Sincethe two records are identical, it is possible to make a single record bythe recording apparatus, and then to reproduce this record displaced theproper amount on the record sheet in any suitable manner. Numerous othersimilar modifications of the invention will occur to those skilled inthe art. ll, accordingly, do not wish to he restricted to the particularembodiment of the invention herein descriloed and illustrated forexplanatory purposes, hut I aim in the appended claims to cover allmodifications within the scope or the invention.

What claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. i i demand apparatus comprising an integrating electric meter havinga rotatable shaft, a time actuated record sheet, aplurality or recordingdevices in contact with said record sheet and displaced from one anotherin the direction of movement or the record sheet, means for moving saidrecording devices transversely of said record sheet at a rateproportional to the rate of rotation of said meter shaft, and means forintermittently returning said recording devices to their initialpositions at one side oi? said record sheet.

2. ll. demand apparatus comprising an integrating electric meter havinga rotatable shaft, a time actuated record sheet, two recording devicesadapted to make marks on said record sheet, said recording devices being displaced from one another in the direction of movement of saidrecord sheet, means operatively connecting said recording de vices tosaid meter shaft, and means for intermittently returning said recordingdevices to their initial positions at one side or said sheet.

A demand apparatus comprising an integrating electric meter having arotatable shaft, a time actuated record sheet, two recording devices incontact with said record sheet and displaced from one another in thedirection of movement of the record sheet, means operatively connectingsaid record ing devices to said meter shaft, means normally tending toreturn said recording devices to their initial positions at one side ofsaid record sheet, and means for periodically interrupting the operativeconnection between said recording devices and said meter shaft wherebysaid last mentioned means operates to return said recording dc vices totheir initial positions.

4. A demand apparatus comprising an integrating electric meter having arotatahle shaft, a time actuated record sheet, and means operativelyconnected to said meter shaft for making two continuous records on saidrecord sheet, said records bein displaced irom one another in thedirection of movement of said record sheet a distance equal to theamount of movement of said record sheet in a predetermined time interval.

5. A demand apparatus comprising an integrating electric meter having arotatable shaft, a time actuated record sheet, a plurality or recordingdevices in contact with said record sheet and displaced from one anotherin the direction of movement or the record sheet, and means operativelyconnecting said recording devids to said meter shaft.

6. A. demand apparatus comprising an integrating electric meter, a timeactuated record sheet, a plurality oi recording devices, meanscoiiperating with said meter for simultaneously moving said recordingdevices transversely of said record sheet an. amount proportional to theamount or metered energy, said recording devices being displaced fromone another a distance equal to the amount or movement of said rechrdsheet in a predetermined time interval, and

means for intermittently returning said recording devices to theirinitial one side of said record sheet.

7. A demand apparatus comprising an integrating electric meter, a timeactuated record sheet, and means coiiperating with said meter forproducing on said record sheet two graphic records of the amounts ofmetered energy, said two records being identical except that every pointor one record .is displaced "from the corresponding point or the otherrecord a predetermined distance in the direction or travel of therecord. sheet.

8. A demand apparatus comprising an integrating electric meter having arotatahle shaft, a time actuated record sheet, a recording deviceadapted to produce two similar records on said record sheet,corresponding points of said two records being displaced irom oneanother a predetermined distance in the direction or movement of saidrecord sheet, and means operatively connecting said recording devihe tosaid meter shaft.

9. A demand apparatus for determining the demand of an electricalinstallation during a predetermined period or time comprising anelectric meter, time actuated recording means, and meanscofiperating'with said meter for producing by said recordingmeans twosimilar records whose coifirdinates are the amount of energy consumedand time, the coiirdinates with respect to the amount of energy consumedof corresponding points on said two records being the same positions attill its

while the coiirdinates with respect to time of corresponding points onsaid two records are displaced an amount determined by saidpredetermined period of time.

10. A demand apparatus for determining the demand of an electricalinstallation during a predetermined period of time comprising anelectric meter, time actuated recording means, and means including saidelectric meter and said recording means for producing two graphicrecords of the \amount of energy consumed with respect to time,corresponding points with respect to time of said two records beingdisplaced in the direction of the coordinate of time an amountcorresponding to said predetermined period of time.

11. The method of determining the demand of an electrical installationduring a predetermined period of time which consists in producing twosimilar records whose coordinates are the amount of energy consumed andtime, arranging said records so that the coordinates .with respect tothe amount of energy consumed of corresponding points on said tworecords are the same while the coordinates with respect to time ofcorresponding points on said two records are displaced an amountdepending on said predetermined period of time, and determining thedemand during the predetermined period of time by comparing thecoordinates with respect to the amount of energy consumption of twopoints on said records having the same coordinate of time.

12. The method of determining the demand of an electrical installationduring a predetermined period of time beginning at any desired timewhich consists in producing two similar records of the amount of energyconsumed with respect to time, and

arranging said records so that the coordinate of any point on one recordwith respect to the amount of energy consumed is the same as the similarcoordinate of the corresponding point on the other record and so thatthe coordinate of any point on the first record with respect to time isdisplaced an amount depending on the predetermined time interval ofdemand measurement from the similar coordinate of the correspondingpoint on the second record, whereby the difference between thecoiirdinates with respect to the amount of energy consumed of two pointson said records having a common coordinate of time is a measure of thedemand during the predetermined period of time beginning at the timerepresented by the common coiirdinate of time.

13. The method of determining the demand of an electrical installationwhich consists in producing two similar records whose coordinates arethe amount of energy consumed and time, arranging said records so thatcorresponding points on the two records have acommon coordinate withrespect to the amount of energy consumed and different cot'vrdinateswith respect to time, the difference in said last mentioned coordinatesdepending upon the period of time during which it is desired to know thedemand, and determining the. demand by obtaining the difference betweenthe coiirdinates with respect to the amount of energy consumed of twopoints on said records having a common coordinate of time.

In witness whereof, I have hereunto set my hand this 1st day ofSeptember, 1916.

JAMES R. CRAIGHEAD.

